Tandem bicycle frame



March 26, 1946.

Filed ,July 26, 1944 I mmeya Patented Mar. 26, 1946 ornce I TANDEM meYcm FRAME- Fra'nk W'. schwinn'fchicago; ll'i. Application July-2G, 1944; semi Nor 541E655 The present invention :relates'to' tandem bicycle frames, and is particularly concerned with a tandem bicycle frame of the type in: which pro vision is made for afemale rider in back of the ma'lerider. In the tandem :bicycle frames of the'prior-ait having provision for the female rider in front of the male rider; the low bent'tubes-at'the-front, which were used to'form the low section of zthat part of the. frame were very" weak, with the te suit that the frame was twisted out of shape easily;

In the'devices of the prior art, in order to even come thisweakness, the 'tandems were provided with heavy cumbersome frames, which were "also unsatisfactory onaccount of their weight; g

One of the-"objects of the present invention-is the provision of an improved tandem- -bic'ycle frame which is light,zyetstrong and rigid, and which is peculiarlyadapted to resist th'eforces which are applied to'abicycle frame of this character with a'minimum amount of twisting and bending;

Another object of theinventionis the provision of i an improved tandem bicycle frame embodying a plurality of truss constructions; one within the other; which strengthen g'reatly-theresistance of the frame to twisting" and bendingyand permit theframeito be'made of relativelylighter tubes than the devices of the'prior art. I

Another ob'ject of the inventionis the provision of a centrally located frame member, the tendency of the rear crank hanger to twist biitof 1 Claim; (c1. 280 -281) the frame being equipped with the usual wheels,

handle banseats; etc: Referring to the drawing; I 0 indicates in'its en tirety the tande'm'bicycle, which isprbvided with an improvedvframe -H constructed according :to the'invention: The bicycle is provided with :the usual f'ront andsrear' wheels- I2, l3, the front and rear-seats; l5 mounted upon the saddle. posts l6, H. The bicycle also includes the usual front handlebars I8 usedfor-steering thev steering wheel l2, buttherear: handle bars -|9-*m'ay be r'nounted upon-the special-saddle post l6 so that steering is done only from the front handle bars. The-frame H includes: the transverse tubular members-writ serving as the front and rear crank hanger-members and provided with the crankshaits 22, 23, the-cranks and pedals, sprockets 24, 25, and chains 26, 21 for driving the rear wheel-|3.- :.1i The front portion of theiframe -l'l is preferably provided with astraight tubular member 28' serving as the saddle post :tube and extending from the saddle post V socket at its-upper j end to the front crank hanger 20. This tubular member 28 is joined to th'ehead tube 29 by the'front't l tube 30; the' frontcenter-tube 3t, andthefront down alignment with the front crank hanger when the bicycle is subjectedto a turning movement under load.

Another object of the invention is the provision of an improved tandem bicycle frame which may be constructed more economically, yet which is stronger for equivalent weight, than the devices of the prior art, and also which can be used for a long period of time without any possibility of the frame being twisted or bent out of shape when subjected to loads for which it has been designed.

Other objects and advantages of the invention will be apparent from the followiig description and the accompanying drawing, in which similar characters of reference indicate similar parts throughout the several views.

Referring to the single sheet of drawings, the figure illustrated is a side elevational view of a tandem bicycle frame embodying my invention,

tube 32, the latter being attached to the front-seat mast tube 28 *atthe front cranlghanger zfl.

The two crank hangers are i oined-bythe bottom tube 33 and thefrontcenter'tube is preferably extended straight, backwardly past thefront seat masttube 28 by means of the rear center tube 3ft, which is attached to the-rear hanger-tube 2 i.- The-rear-seat mast tube is attached-atits lower end to the rear-crank hanger tubel I, and has an upwardly i and rearwardly-extending POT-,- tion 36, which;has-a rearward bend at '31 and an upwardly and rearwardly extending straight por tion 38.

The bend at 31 provides an offset which brings the saddle l5 back behind the rear hanger 2| in proper position relative to the pedals, while still maintaining the central portion of the tandem frame I l in substantially the form of a paralleloram.

The rear saddle post tube 35 is joined to the w front saddle post tube 28 by the rear top tube 39, and the direction of this rear top tube 39 is preferably such that the lower rear stays 40 extend in substantially a straight line in the same direction rear shaft 4|, -and this same flange 43, which is slotted to receive the shaft 4|, is also integrally joined to the two rear fork members 44, which have their forward ends secured to the rear is stronger against twisting action than the devices of .the prior"art, du e to theattachmerit of; the'rear top-tubefl39 to the rear seat mast-tube 35 at a relatively high point, as distinguished from the devices of the prior art, in which there wasamuch lower point of attachment I Forces applied'to the frame in the form less tendency to twist the frame than when a turn is being made. The rear wheel axle is firmly. held between its rear stays and forks, but the.frontzwheelis'held in a fork, which must be .pivot'ally' mounted in the head tube in'thefrontp'art ofthefframe. "The center'of gravity isvery high, as the riders sit on saddles mounted above;the top of the frame; and thisinduces atendenc'y for the .frameto twist sidewise because there is no firm support for'the front end. a iT The axis of pivotfor steering extends forv'vardlyand' downwardly, and placesacompression on the front top tube 30 and a tension on the front down tube 32. When, however; the front wheel is turned, the outwardly projecting front fork '45 locates the point of support 41 of 'the'front wheel at a considerable distance laterally' of the frame, and the tendency is toward :a twisting of the This is, of course, resisted by the front-top tube 30 and front down tube-32, but the front center tube 3 I, which is extended in therear centertube 34 to the rear hanger? l,*is perfectly located to resist this twisting movement by a direct torsional resistance; ""3 P Such tubes have a much strongerresistance to torsion than they do -to bending; Before the rear hanger 2| can be twisted 'outof-li'ne so'as to per mit therear whee'l to become out of line, both of the tubes'3|,'3'4 wouldh'ave to be subjected to a very powerful torque, which they are well adapted-to resist. f a i v 1 Furthermore, the center tub'es 31,34 'are well located to lee-subjected to a compression when the bicycle frame'is under load, and the low erpart of the bicycle [frame 33, comprising the members 3l 32 28, and '34,;form a double truss; which provides a maximum strength for'thisp'art, of the fra e f I '5 Another truss-like arrangement is comprised by the tubular members 30, 3|, 28, 29, 34 and 36, and the upper members of these trusses are subjected mainly to compression.

It will thus be observed that I havean improved tandem bicycle frame which, for the same amount of metal or weight of its tubular members, is stronger and adapted to resist the bending and torsional forces that are applied to such aeframe when it is subjected to load.

The present cycle frame maybe made much lighter in weight than the tandem bicycle frames of .the prior art, while still being adapted to support relatively great Weight without undue twist- '15 weight-on the sides [4, l5 are resisted byupward thrust at the wheel axles 4|, 45; and Whenthe' bicycle is proceeding in a straight line, there is ing or bending. Twisting or bending action is substantially eliminated so that it is scarcely noticeable.

" -While I have illustrated a preferred embodiment. of my invention, many modifications may ent of the United States, is?

In a tandem bicycle, the combination of an upwardly and rearwardly extending head'tube carrying a steering post and a steering wheel, the said'head tube being joined solely to three rearwardly extending tubular frame members located in substantially the same axial'plane, the

said rearwardly extending frame members comprising a substantially horizontalfront top tube, a downwardly and rearwardly'e'xtending front center tube, and a front down tube, the front down tube carrying a crank hanger tubewhich is joined to a seat'post mast tube which extends upwardly and rearwardly and is'jjoined' to the fronttop tube and front center tube, the frame also including a direct axial extension of the front center tube rearwardly and downwardly to a rear crank hanger tube, which crank hanger tubeis also joined by a horizontal bottom tube to :the first-mentioned crank hanger tube and by aseat post mast'tube to a reartoptube; which rear top tubeextends rearwardly and downwardly;'in alignmentwith a rearwardlyiand downwardly extendingrear fork, the rear crank hanger being also joined to a lower rear fork; and there being an upper fork which is-joined to the rear seat post masttube, all the rear forks'having their legs which are on the same side joined together at a rear shaft support. 7

FRANK W. SCHWINN.

invented 

